That did the trick!
I'm not always online to approve a comment right away, which is why I wanted a user logged in and registered to comment. There must be a problem with that script because even if they were registered and logged in, it still would not provide the comment form.
I also had "Comment author must have a previously approved comment" checked as well. That way, if someone had already commented before, I would know it was pretty likely it was not spam, and the comment would go through without my having to check it first.
I believe my requirements are satisfied by unchecking the "you must be logged in and registered to comment", and checking the option to require an email address. I kept checked the "Comment author must have a previously approved comment" which I believe will hold it until I have a chance to review the comment.
Thanks so much for your help!